FIG 5.

Disrupting LPS core biosynthesis induces morphological defects in E. coli. (A) Maturation of Und-PP-linked O-antigen intermediates and their ligation to the lipid A core. Mutations that truncate the core oligosaccharide (e.g., ΔwaaC) prevent attachment of the O antigen (right). Abbreviations: OM, outer membrane; A, lipid A. The definitions of the other abbreviations are listed in the legend to Fig. 2. (B) General structure of the E. coli K-12 core oligosaccharide (shaded in gray) (reviewed in reference 77). WaaC and WaaF transfer Hep-I and Hep-II, respectively, onto the growing O-antigen chain. (C) Micrographs of cells with the indicated genotypes. Cells were grown and imaged as described in the legend to Fig. 2. The cells were fixed and photographed by phase-contrast microscopy. Bar, 3 μm. Similar results were obtained for mutants of waaF, as shown in Fig. S5 in the supplemental material. (D) Flow cytometry data from live cells in panel C. Histograms of the FSC-A from 100,000 events (cells) are shown. The mean cell size of the wild-type strain (red graph) is represented by the dashed line and is expressed in arbitrary units (AU). Data are representative of those from two independent experiments. The strains tested were MAJ330 (wild type), MAJ374 (ΔwaaC), MAJ343 (ΔwecA), and MAJ384 (ΔwecA ΔwaaC).